He's probably referring to audio test tones. They are sine-wave pure tones generated at specific frequencies to allow you to test the quality and strength of those frequencies on your playback hardware and speakers/headphones.

Here is a site with 5 test tones from 100Hz up to 10KHz. Not really good for bass response tests but good for some lows, all the mids and some of the highs. Downloads are in WAV and MP3 format and are in either 5 or 30 second clips.

Here is another page with more test tones to download in WAV and MP3, which include pure solo frequencies from 10Hz to 15KHz (perfect for those high-end cans and IEMs that can rattle your sternum loose) in and out of phase, as well as full sweeps, EQ tests, stereo imaging tests, pink/white noise tests, and so on.

They're not really useful for the average Joe except as a matter of curiosity, but audiophiles can use these to give their kit a good workout to see how they respond across the spectrum.

If you're looking for actual music to give your cans a good test run, may I suggest "Underground" by Shakta? (From the double album "Feed the Flame") Deep, resonant bass notes, lots of stereo effects, sweeps and pans, subtle but crisp highs -- really good for an all-over real-world audio test.

Actually, most of the first CD of "Feed the Flame" makes for a good test bed.

I'd definitely recommend Mindfield's solution for a pure bass test. However, if you want to test it out with songs I'd recommend anything by the Blue Man Group.

If you aren't familiar with them, they are a non-talking performance group that plays mainly percussion instruments (they're backed up by a band). They have a CD with vocal songs called the Complex, but I prefer Audio, their instrumental album.